libctf, create: fix ctf_type_add of structs with unnamed members

Our recent commit to support unnamed structure members better ditched
the old ctf_member_iter iterator body in favour of ctf_member_next.
However, these functions treat unnamed structure members differently:
ctf_member_iter just returned whatever the internal representation
contained, while ctf_member_next took care to always return "" rather
than sometimes returning "" and sometimes NULL depending on whether the
dict was dynamic (a product of ctf_create) or not (a product of
ctf_open).  After this commit, ctf_member_iter did the same.

It was always a bug for external callers not to treat a "" return from
these functions as if it were NULL, so only buggy callers could be
affected -- but one of those buggy callers was ctf_add_type, which
assumed that it could just take whatever name was returned from
ctf_member_iter and slam it directly into the internal representation of
a dynamic dict -- which expects NULL for unnamed members, not "".  The
net effect of all of this is that taking a struct containing unnamed
members and ctf_add_type'ing it into a dynamic dict produced a dict
whose unnamed members were inaccessible to ctf_member_info (though if
you wrote that dict out and then ctf_open'ed it, they would magically
reappear again).

Compensate for this by suitably transforming a "" name into NULL in the
internal representation, as should have been done all along.

libctf/ChangeLog
2021-01-19  Nick Alcock  <nick.alcock@oracle.com>

	* ctf-create.c (membadd): Transform ""-named members into
	NULL-named ones.
	* testsuite/libctf-regression/type-add-unnamed-struct*: New test.

1 files changed, 6 insertions, 0 deletions

diff --git a/libctf/ctf-create.c b/libctf/ctf-create.c
index 651d39d..50f48eb 100644
--- a/libctf/ctf-create.c
+++ b/libctf/ctf-create.c
@@ -2403,6 +2403,12 @@ membadd (const char *name, ctf_id_t type, unsigned long offset, void *arg)
   if ((dmd = malloc (sizeof (ctf_dmdef_t))) == NULL)
     return (ctf_set_errno (ctb->ctb_dict, EAGAIN));
 
+  /* Unnamed members in non-dynamic dicts have a name of "", while dynamic dicts
+     use NULL.  Adapt.  */
+
+  if (name[0] == 0)
+    name = NULL;
+
   if (name != NULL && (s = strdup (name)) == NULL)
     {
       free (dmd);